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View Full Version : bungee vs. catapult


inedesca
12-18-2005, 06:01 PM
Seems that people prefer bungees vs catapult, but I wonder if catapult is not more reliable.

On the other hand, we know that the correct bungee tension must be about 5 times the model weight; but what for catapults, should be also 5 times?

cyclops2
12-18-2005, 06:20 PM
I have never seen a catapult. But, I assume they are not as gentle to the planes structure as a bungee?
I have seen 50' bungees for the gliders. They are operated by a guy in a golf cart for retrieve and launch.
He is fully protected all the time. Neat.

panzerd18
12-20-2005, 10:27 PM
I have a real bungi cord to high start my glider. Its not rubber and string but all nylon type fibre wire stuff.

cyclops2
12-21-2005, 02:59 AM
Panzer. I would place the HI-STARTS as a catapult.
The throttle pedal man decides if your wings fold or not.:D :confused: :eek:

panzerd18
12-21-2005, 07:07 AM
I know a guy who is a bit crazy in his old age, as he did too many drugs in his youth and scrambled his brains. He got banned from operating the winch on real life gliders as he couldn't take his foot off the pedal because his leg cramped up.

lindart aviation
12-21-2005, 06:32 PM
My catapult uses two 1/2" x36 poplar dowels 9" apart in a section of 2x4 pine. LARGE nails anchor it. A 20' length of small size hi-start rubber with an anchor ring on one end and a 10' twine string with a ring at the other end comprise the basic launch device.A second ring is located far enough forward on the string to let the plane set on the catapult with-out the tail feathers touching the base. The catapult is angled 10 degrees up.
The end ring is placed in a slot in the 2x4 that has a loose fitting vertical pull pin.This is servo actuated with a second receiver/battery that I trip with the retract switch on my transmitter when ready to launch.
The hook is located just ahead of the C/G and the line tension is set at 8-10 # for a GWS Spitfire.
The plane is off in a literal blur!!! I throttle up after it comes off the line.

I am an old guy with a torn shoulder joint,thus the catapult. A friend has a duplicate for an E-powered Hellcat that couldn't be launched with a good shoulder.
FWIW. art

inedesca
12-22-2005, 06:29 AM
These are to me catapults.

Portable, easy to direct quickly into the wind, angled at about 30+ deg and powerful

lindart aviation
12-22-2005, 07:53 AM
inedesca,you are correct,these are true catapults.They are self contained. My set up is a modified high start.
I stand corrected and am going to build one based on your photos.
Thanks, art

inedesca
12-22-2005, 03:14 PM
I am finishing one and I will upload the plans these days.

Now let me tell you, when it comes to launching low wing models what I have been doing so far is that I put three small pieces of tirplay under the wing as to form a tirangle, two aligned with the c.g. for the middlefinger and thumb and one behind for the index, so I grasp it as a Bowling ball, and so far I have launched my planes succesfully, and they are so small that they go unnoticed, but of course a catapult is more convenient although more cumbersome.

In the photos you can see this configuration for a GWS Corsair

cyclops2
12-22-2005, 06:56 PM
I like the last one on the right. It looks adjustable for wing thickness and always releases at a fixed wing angle of attack. Great design:)

jrb
12-22-2005, 09:17 PM
Plans?

inedesca
12-22-2005, 11:05 PM
Drawings, alright?

Daren Savage
04-28-2006, 06:50 AM
These are to me catapults.

Portable, easy to direct quickly into the wind, angled at about 30+ deg and powerful

We built the catpult seen in the photo with my F-4 Phantom II. It was based upon the kit from the now defunct Warbirds, Ltd.

We replaced the bungee cord with 3/8" Dripped Mandrel Latex (DML). DML is IMHO the best material to use for catapults or bungees. We also bungee launched these jets, again using DML.

We also changed to larger rollers on the front to accomidate the larger diameter of the DML, as well as added a custom rear pulley system and improved the latching lever.

The bungee pulls the models to a much higher speed than the catapult, but the catpult is much more portable. The catapult is consistant, giving exactly the same toss every time. There is no worry about the infamous Bungee Death Roll with the catapult.

Mostly I think it depends on your needs. Bungees are nearly impossible to use with tractor propeller models. The combat catapults, use special cradles to hold the wings for launching.

Daren

Daren Savage
04-28-2006, 06:52 AM
I like the last one on the right. It looks adjustable for wing thickness and always releases at a fixed wing angle of attack. Great design:)

That's the stock Warbirds, Ltd. cradle that we modified for our edfs.

Daren

Boomerang
04-28-2006, 08:44 AM
A friend has built a half bungee, half catapult for his turbine powered park flyer. It's a short bungee with a holding cradle for the model, much more reliable than hand launching. - John.

jrb
07-05-2006, 04:13 PM
Have been launching my T-33 via bungee since 99; during warm weather only – bungee (latex tube) doesn’t do well when its cold. That’s a lot missed flying time here in the upper Midwest; and its nice to belly flop on snow.

Inspired by edfrules, I built and now have successfully launched my T-33 via an Air Catapult!

Details can be found here: http://www.rcgroups.com/forums/showthread.php?t=524127 .

Sorry no video of the T-33 being launched, but here a test with a 7lb-13oz plank @ 80 & 100psi: http://www.rcgroups.com/forums/showthread.php?t=527873 .

jrb
07-17-2006, 02:29 PM
More videos uploaded!

jrb
07-23-2006, 04:36 PM
http://www.rcgroups.com/forums/showthread.php?t=543377#post5759170

jrb
08-09-2006, 03:58 PM
Most recent video added; results with shock cord loop were very successful, analysis of the crowd is that it makes the system better!